The invention relates to an optical code converter for OCDM.
The invention is based on a priority application EP 01 440 274.7 which is hereby incorporated by reference.
OCDM systems comprise optical filters that are used, inter alia, for encoding and decoding optical signals. OCDM is also described as OCDMA; OCDM=optical code division multiplex, OCDMA=optical code division multiple access. OCDM is based on spectral encoding of broadband optical sources. The light of an LED modulated with data to be transmitted is passed, for example, through an optical filter and encoded in this way; LED=light-emitting diode. A plurality of said LEDs and optical filter combinations is connected at the transmitter end, for example, via an optical coupler to an EDFA that is connected to an optical glass-fibre line; EDFA=erbium-doped fibre amplifier. In this way, variously encoded optical signals are generated that are transmitted together in amplified form via the glass fibre. A transmission to a plurality of receiving ends can take place via optical splitters. Each receiving end comprises, for example, a differential receiver having an appropriate optical filter for decoding the optical signals intended for the receiving end.
An optical filter is designed, for example, as Mach-Zehnder filter. In the Mach-Zehnder filter, the received OCDM signal is forwarded via two paths that have complementary transmission functions. The Mach-Zehnder filter can be used both for encoding and for decoding OCDM signals.
At the transmission end, an optical filter is used, for example, for each optical transmission channel. The optical filters must be tuned well with respect to one another in order, for example, to reduce crosstalk. At the receiving end, an optical filter is used, for example, that is tuned to the optical transmission channel provided for the receiving end. Alternatively, the same number of optical filters is, for example, used at the receiving end as at the transmitting end. The optical filters at the receiving end are tuned to the optical filters at the transmitting end.
In OCDM systems, optical signals have hitherto been transmitted to the receiving end in the optical transmission channel assigned at the transmitting end. This type of transmission is rigid and makes possible only simple network topologies, such as, for example, point-to-point.
An object of the invention is to make possible a flexible allocation of channels.
This object is achieved by an optical OCDM code converter for converting an optical signal from a first optical transmission channel to a second optical transmission channel, comprising a series connection of a first (decoding) optical filter for filtering the first optical transmission channel, an optical coupler and an optical broadband source and a second (encoding) optical filter for filtering the second optical transmission channel that is connected to the optical coupler, wherein the second optical transmission channel differs from the first optical transmission channel.
The code converter according to the invention is notable for a simple and efficient type of code conversion in an OCDM system, which code conversion may be used, for example, for optical routing. This makes possible the construction of OCDM systems having flexible topologies. Optical routers are sited at network nodes and perform optical routing, for example for the purpose of setting up optical Internet connections. The OCDM system may be used, for example, as an optical transmission network and/or an optical switching network. Via the OCDM system, for example, SONET, SDH, ATM, VoIP, IP, DSL, voice, data or video signals can be transmitted; SONET=synchronous optical network, SDH=synchronous digital hierarchy, ATM=asynchronous transfer mode, VoIP=voiceover Internet protocol, IP=Internet protocol, DSL=digital subscriber line.
In an advantageous refinement of the invention, both a code conversion and a wavelength conversion are possible. This extends the degree of freedom in allocating signals to transmission channels in various wavelength bands so that still more complex network structures are made possible.
Advantageous refinements are to be found in the dependent claims and the description below.